How Plastic Welding Works
Just like metal workers use heat to join two pieces of metal, plastics engineers use heat to meld two pieces of plastic. Unlike in the heavy metal manufacturing plant, though, plastics engineers don't use intense, open flames to melt their materials. The process is refined and precise, allowing them to create tiny, tight seals that are strong enough for use across industries.
For example, something as simple as an inflatable beach ball is made using plastic welding—it holds the multi-colored pieces together and forms a seal tight enough to hold in air, even when you're giving it the old "bump, set, strike." It isn't all fun and games, though. Plastic welding is such a consistently precise and strong method of joining materials that the healthcare industry and even the military count on it for manufacturing their products. Plastic welding keeps bacteria out of hospital IV bags and blood bags, and it forges a seal strong enough to make military gun bags completely watertight.
It isn't as simple as putting flame to material, though—in fact, there are different types of plastic welding that manufacturers use so that they can make the products you rely on every day. These are just a few.
Heat isn't always part of the equation when you're melding plastics. Solvent bonding is a method of plastic sealing that uses heat sometimes, but not always. At other times, it relies strictly on chemical manipulation. Solvents are applied to the plastics, they're joined together, and that's that—but it's more complicated than it sounds. Chemical solvents aren't like what you find in a tube of glue. Instead of just slathering on a sticky substance that creates an imperfect bond, the solvents used in industrial manufacturing alter the materials to which they are applied.
When solvent is applied to the plastic, it ever-so-slightly dissolves the outermost layer. As the materials are dissolving, they are pressed together, and as the dissolution of molecules stops, they are stuck together.
Radio Frequency Welding
Radio frequency heat sealing, or RF welding, is another method of welding that takes root in science rather than heat alone. During this process, which can be used for PVC welding and other plastics and acetates, the two pieces of material that are to be joined are pressed together using high pressure. As they are held together, a die moves into place over the plastic and is positioned right where the weld is going to be.
The die is used to direct high frequency waves, which shoot through the plastics. When this happens, their molecules start to heat up, move around and mix together. After they stop, they're all mixed up together and out of order, making them connected. Think of it this way: Compare the molecules to jelly beans. If you fill a jar partially with one color of jelly bean and partially with another color, they stay separated—just like the two plastics under pressure. If you shake them up, though, they mix together, and when you stop, they aren't separated at all anymore. This is what happens during the RF welding process.
Hot Air Sealing
Hot air sealing is a type of welding that uses heat, but not necessarily flame, to conjoin plastics. Instead of using a direct flames to heat the plastic, like you would when you weld metal, it uses compressed air. Compressed air is like what you use to fill a car tire—it comes out fast, under high pressure and in a small, concentrated stream. A machine that pumps out compressed air is aimed at the plastics that are going to be welded, and as the air shoots out, it is heated. The result is a precise, high-pressure stream of air that is hot enough to melt plastics and forge them together.
Hot Wedge Welding
A heated object melts plastic—even walking on pavement that's hot enough will melt the soles of your shoes. This same principle is behind hot wedge welding, albeit with much more accuracy. During this process, a tool shaped like a wedge is heated to extreme temperatures. When it's pressed against the plastic, then, it melts the materials together. This happens almost instantaneously, allowing the machine to process large jobs relatively quickly once it is set up. Because this and hot air sealing are both heat sealing services, they are easy to mix up—just remember that hot wedge welding actually connects with the material, while hot air sealing doesn't.
Other Types of Welding
These are just a few types of welding that are used in plastics engineering. There are other types, as well, like laser welding. This is a process in which two materials that respond differently to laser beams are pressed together. When a laser beam passes through them, they heat up and weld together. Processes like this, RF welding and the various other types allow manufacturers and engineers to create the products that we use on a regular basis, and to make them so secure that we never have to worry about them.